| The growth conditions and material design factors related to optimizing the two-dimensional electron gas (2DEG) conductivity of InP-based composite-channel high electron mobility transistor (HEMT) structures were investigated through a comparative study of the 2DEG properties of various InP-based HEMT structures, such as conventional InAlAs/InGaAs HEMT structures and lattice-matched InAlAs/InGaAs/InP and pseudomorphic InAlAs/InAsP/InP composite-channel HEMT structures grown with solid-source molecular beam epitaxy (SSMBE). Several approaches, such as channel doping, the inclusion of InGaP hole barriers, and Al-rich InAlAs Schottky barriers were combined with the InGaAs/InP composite-channel HEMT structure to enhance breakdown voltage. The device performance fabricated with the optimized InGaAs/InP composite-channel HEMT structure showed excellent DC characteristics and state-of-the-art RF power performance at W-band. Furthermore, a study of the 2DEG properties of pseudomorphic InAsxP1–x /InP composite-channel HEMT structures was carried out. Structure variations included the effects of As composition (0 < x < 0.74), channel thickness, InAlAs spacer thickness, arsenic and phosphorus flux switching scheme at the interfaces, doping scheme, and strain compensation (In1–xGaxAs, x > 0.53/InAs0.6P 0.4/InP). The 2DEG conductivity results showed the great potential of the InAlAs/InAsxP1–x/InP material system for microwave and millimeter wave power applications. |
